Wind turbine generators may be operated in partial and full load modes. In partial load modes the objective is to optimise power production from a given available amount of wind energy. In full load modes the objective is to produce the nominal power of the wind turbine generator.
It is known to use different control schemes in order to control the wind turbine generator in the different load modes. Accordingly, switching between the different control schemes is required as the wind velocity varies between low wind velocities where the wind turbine generator should be operated in the partial load mode and high wind velocities where the wind turbine generator should be operated in the full load mode. Such switching may have undesirable effects on structural loads, utilisation of the wind energy and other operating conditions of the wind turbine generator.
Thus, it is a problem that known control schemes may have difficulties in dealing with switching between different control schemes.
WO2011/076295 discloses a wind turbine having a control method and controller for performing predictive control of a wind turbine generator. Based on the measured instantaneous wind speed, it is known to provide control signals to a wind turbine in order to control the pitch of the wind turbine rotor blades and the speed of the generator. However, it is difficult using instantaneous wind speed measurements to achieve smooth control, due to finite response speeds of the associated electro-mechanical systems, as well as the constantly changing control system inputs. The predictive control system described in the application assumes a model of generator speed based on the values of the incident wind speed v(t) and the values of a control signal u(t) output to the wind turbine in a feed forward loop. Here, the control signal can be for one or more of controlling either the power setting of the generator, or the pitch angle of the rotor blades. The predictive controller uses a rolling time series of values for v(t) and u(t) and based on a predicted response of the generator speed w(t) optimises the time series control signal u(t). The predicted response of the generator speed w(t) is based on model, that can be refined in real time as the wind turbine operates.
The inventor of the present invention has appreciated that improvement in wind turbine controllers is of benefit, and has in consequence devised the present invention.